1. Field of the Invention
The present invention relates to a method of sample preparation for transmission electron microscope analysis, and more particularly to a method of photoresist sample preparation for transmission electron microscope analysis.
2. Description of the Related Art
In the analysis of an ultra large scale integrated (ULSI) circuit, the profile images of an ULSI circuit sample are crucial. Particularly, as the dimension or the line width of the ULSI circuit advances to a scale under 0.2 micron, the profile images showing direct and strong evidence of various process results are the keys of further process technology development and the bases of solving various processing problem resulting device failures. A scanning electron microscope (SEM) is one of the most commonly used analysis tools of the semiconductor industry today. But the applications of the SEM on modern ULSI circuit technology have met limitations due to their resolution maximum which is about 12 angstroms. In order to clearly find the tiny features of modern semiconductor devices, a transmission electron microscope (TEM) is used because of its high resolution which is up to 1.4 angstroms. However, the TEM analysis still cannot be available in some situations, where for example, the sample being analyzed has photoresist material, and more particularly as a patterned photoresist layer of a sample itself is the main object being observed. Using a TEM to analyze a patterned photoresist layer having tiny features overcomes a problem resulting from the sample preparation process comprising a slicing process, a grinding process, a polishing process and a cleaning process. Furthermore, the slicing process using a focused ion beam (FIB) definitely causes damage to the photoresist layer and breaks the characteristics. Moreover, the cleaning process using an organic solvent to clean the sample renders the TEM analysis on a photoresist layer impractical since the organic solvent such as acetone will completely destroy the features.
Another problem of a TEM analysis on a photoresist layer results from the dimension distortion of the photoresist layer which appears in moisture and oxygen-contained environments. The dimension distortion of a patterned photoresist layer being observed will make the efforts of further process technology development uncertain since the true dimension of the defined pattern used to form tiny contact or via holes or gate electrodes is crucial as the line width or the technology level of the integrated circuit of the next generation advances further. Furthermore, still another problem of a TEM analysis on a photoresist layer results from the electron beams used to form images of the TEM since the electron beam bombardment which effectively acts as a heat source causes the photoresist layer to shrink.
Therefore, it is necessary to provide a novel TEM sample preparation technology to solve the problems mentioned above.
It is therefore an object of the invention to provide an analyzable photoresist sample for transmission electron microscope (TEM) analysis.
It is another object of this invention to provide a method of a TEM photoresist sample preparation without the charging problem and FIB slicing damage.
It is a further object of this invention to provide a TEM photoresist sample having a true dimension and render the clear profile observation and the precise dimension measurement of a defined photoresist layer used to define a deep submicron semiconductor device practical.
To achieve these objects, and in accordance with the purpose of the invention, the invention uses a conductive layer and a dielectric layer to protect a photoresist layer of a TEM sample. Both the conductive layer and the dielectric layer are formed by a physical vapor deposition process at a temperature in which the photoresist layer remains stable. During the sample slicing and the TEM observation process, the dimension of the patterned photoresist layer could be maintained. Thus the clear profile observation and the precise dimension measurement of the patterned photoresist layer will be practical.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.